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Is the card still readable in the PC? if so, copy all photos off to a folder on the PC, try reformatting the card, and see if it is still usable at all.
But in the end, you will be better off buying a new card, since this one has seen a lot of use and has at last failed.
If the card is not readable in the PC either, then surely you copied all photos off of it already, to the PC? or did I misunderstand that part?
Also, if the cards are working on the PC but not on the camera, you may simply have a defective memory card slot, I'm sorry to say. That can happen, what with frequent swapingout and in of the memory card sometimes transferring static discharges into the slot, which can eventually cause it to cease working.
Your memory card slot should be examined, as to whether any dirt or loose debris of any sort is in it, or perhaps broken or bent pins... a new memory card tried in it to make sure it is the slot and not the memory cards... then you would have to decide between having it repaired, or replacing the camera.